Video here: https://skillsmatter.com/skillscasts/11903-an-introduction-to-event-sourcing
Slides here: https://speakerdeck.com/mottalrd/an-introduction-to-event-sourcing-for-rubyists
Code here: https://gist.github.com/mottalrd/52a99a0a67275013df5a66281a4a1b11

Event sourcing is a design pattern to build applications that are domain centric and easy to extend. The pattern is based on the usage of a persistent event log which substitutes the more classical relational database model for Rails applications.